Naphtha blends, which can include fluid catalytic cracked naphtha, coker naphtha, straight run naphtha, or a combination thereof, are difficult to process. Such blends typically contain olefins in concentrations of 10-50% by volume. The olefins quickly saturate in the reactor bed upon contacting the reactor catalyst. Further, the olefins contacting the reactor catalyst results in an exothermic olefin conversion reaction, releasing substantial amounts of heat and causing the temperature of the first reactor bed to increase dramatically. Such temperature spikes can lead to deactivation of the first catalyst bed and often leads to difficulty in controlling temperatures in subsequent beds as well. Moreover, bed deactivation can cause the reactor to operate at less than its maximum efficiency, lowering the amount of cracked material that is processed by the unit or limiting the duration that the unit can operate.
One way to compensate for the temperature spike caused by the olefin conversion is to lower the charge heater outlet temperature. This can help, but still results in a temperature difference across the top reactor bed of 60° C.-120° C. However, turndown limitations of the charge heater restrict the capability to lower the charge heater outlet temperature.
Accordingly, there is a need for a process to regulate the temperature across the first bed consistently without disrupting function of the additional beds.